When a surgeon performs a cervical discectomy, prior to cutting into the disc, since under most circumstances all discs look the same from the front, it is common practice for the surgeon to surgically expose the disc and then place a hollow radiographically opaque needle into the suspect disc and then X-ray the disc and needle to make sure the needle is in the proper disc. On hopes that the needle is going into the disc to be removed, however, errors frequently occur and the disc in which the needle is placed will turn out to be a perfectly healthy disc, and the disc desired to be removed will have been one either higher or lower. When the proper disc is located a dye is injected through the hollow marker needle into the disc.
Inasmuch as one is not assured prior to obtaining the radiograph that the marker needle is in the correct disc, it is desirable to use a marker needle of the smallest possible caliber so that in the event it should prove to be in the wrong disc, the disc itself will not have been harmed by the marker needle. Quite obviously, the placement of a large, thick, heavy needle through the casing of the disc and into its substance is harmful.
At the same time, while it is desirous for the reasons already discussed to use a marker needle of small caliber in entering the disc, it is necessary to use a marker needle of as heavy a caliber as possible so that it will show up clearly on the radiograph. This creates a conflict since presently available spinal marker needles maintain the same internal and external diameter from tip to end.
Another set of problems concerning the use of existing marker needles deals with the fact that the approach, for example to the cervical spine, is actually from a lateral aspect to a midline structure. Therefore, when one is working on the front of the cervical spine but approaching it laterally, it is possible to maintain the overlying structures out of the way only by retracting them with either hand held or self-retaining retractors.
The retractors cannot be left in place for the radiograph as they are metal, and they would obscure the marker needle itself. Therefore, when the retractors are removed there is a strong tendency for the midline cervical structures to want to return to their normal location, thereby dislodging the marker needle from the disc. Such a dislodged needle is then useless as a marker and threatens with penetration the vital structures of the neck.
The marker needles that are used for this purpose at the present time typically tend to be about 8 centimeter long spinal needles, and these marker needles have no real capability or special innovation to resist such dislodgement. There is a tendency on the part of the surgeon to try to place the needle as deeply into the disc as possible to stabilize it. However, the surgeon is always fearful of over penetrating the disc and pithing the spinal cord, possibly paralyzing the patient. Thus, there are conflicting desires, that is, the desire to place the marker needle deeply within the disc to provide stability to the needle, and the desire to avoid over penetration of the disc and pithing of the spinal cord. The difference between a good deep placement and pithing the spinal cord may not be more than several millimeters.
At the present time, most surgeons clamp the spinal marker needle with a hemostat or bent mosquito-type hemostat approximately a centimeter from the tip, thereby attempting to provide for approximately one centimeter of penetration of the needle tip, avoiding over penetration. However, the placement of the clamp about the marker needle contributes to the problem of the marker needle dislodging, for the clamp itself has both mass and occupies space. Therefore, when the muscles and the midline cervical structures fall back into place, they tend to pull against the clamp, only complicating the problem of keeping the marker needle upright. Furthermore, as these clamps are not truly designed for the purposes which they are being used, there is the danger of the clamp popping off of the marker needle, and the marker needle then being pushed into the spinal cord.
The next step in the process of obtaining the radiograph is that an X-ray machine must be brought in and placed close to the patient's neck and the operating area. Since the operating area is sterile, and the X-ray machine is not, a large drape or sheet is placed over the operative field. As the marker needle is now the highest object on the field, the sheet frequently comes to rest onto the spinal marker needle and presses against it. This presents a potential danger to the patient, as the marker needle can over penetrate if the clamp should come off.
After the marker needle is utilized to locate the correct placement for the surgical incision or the appropriate disc, a dye (indigo carmine, functional or equivalent) is injected by a syringe into the disc, coloring the nucleus of the disc so that the physician can make sure that all of the pathological disc has been removed.
Typically, it is necessary for the operating room nurse to go to another location to obtain said dye, which is maintained in bulk, and the operating room nurse must then pour the dye into the syringe. The sterility of the marking dye is accordingly compromised.
Further, a second dye typically used in an operating room is methylene blue dye, which is neurologically toxic. These two agents are packed in similar appearing containers. A mix-up by the operating nurse between the two dyes could result in paralysis of the patient.